The metabolites of 4-chlorobiphenyl (MCB) and 4,4'-dichlorobiphenyl (DCB) were isolated and cleaned-up using thin-layer chromatography. The metabolites were then identified. The MCB metabolites were found to be 3-hydroxy-4'-chlorobiphenyl, 4-hydroxy-4'-chlorobiphenyl, 3,4-dihydroxy-4'-chlorobiphenyl and either 3-hydroxy-4-methoxy-4'-chlorobiphenyl or 3-methoxy-4-hydroxy-4'-chlorobiphenyl. The DCB was metabolized largely to 3-hydroxy-4,4'-dichlorobiphenyl and to a minor amount of 2-hydroxy-4,4-dichlorobiphenyl.